Sorry, never heard of that but my first thought would be a skin allergy of some sort. The other thing I might consider would be a displacement behaviour. eg- Deli our dali has an area on her back leg which she has licked raw and we think she started this behaviour because of the wart on her eye, which she couldn't get to. She still licks it occasionally, I think because it is now a habit, parrots do the same thing with feather plucking.